Electrolysis installations in accordance with the above preamble are already known. A prior art installation of this type is shown schematically in the appended FIG. 1. The diagram shows a pressure chamber 3 enclosing an electrolysis stack 5, a first separator 7 and a second separator 9. It will be noted in this regard that in some variant embodiments of these installations, the pressure chamber can be omitted. A double recirculation circuit 11, 13 is provided to supply the electrolysis stack with electrolyte (in the present case, water in which a suitable substance, such as potassium hydroxide for example, is dissolved. The recirculation circuit 11, 13 is a double circuit. It is formed of a cathodic circuit 11 passing through the cathodes of the electrolysis stack, as well as an anodic circuit 13 passing through the anodes. The two circuits 11 and 13 have a shared portion that passes through a recirculation pump 15. The purpose of the pump 15 is to circulate the electrolyte in a loop in the double recirculation circuit 11, 13. Upon exiting the stack 5, part of the electrolytic solution is taken into the cathodic circuit 11 as far as the first separator 7, whilst the rest of the solution is taken into the anodic circuit as far as the second separator 9. The liquid taken from the cathodes to the first separator 7 contains gaseous hydrogen. Similarly, the liquid taken from the anodes contains gaseous oxygen. The separation of the liquid and gas takes place in the separators 7, 9. The degasified liquid is then returned to the recirculation pump 15.
The hydrogen and oxygen accumulate in the respective upper parts of the two separators. The first separator 7 is provided with a pressure regulation valve 17, which determines the working pressure of the installation as a whole (generally between 5 and 30 bar). When the pressure inside the separator 7 reaches the limit value of the valve 17, the valve allows the hydrogen that has been produced to escape. Because oxygen continues to accumulate in the second separator 9 during this time, the water level in the separator decreases and, in accordance with the principle of communicating vessels, the water level inside the first separator 7 increases. The two separators are each provided with a level gauge (denoted as 19 and 20 respectively). The second separator 9 is further equipped with a pressure relief valve 23, and when the gauges indicate that the difference in level in the separators has exceeded a predetermined value, the valve 23 opens and allows oxygen to escape until the two levels become equal.
The operation of the electrolysis installation involves progressive destruction of the water, which it contains. When the sum of the water levels in the two separators falls below a predetermined value, hydraulic supply means are triggered to supply cold water to the recirculation circuit 11, 13. As is shown in FIG. 1, the hydraulic supply means comprise a reservoir of deionised water 25 and a pipe 28 that connects the reservoir to the recirculation circuit. A supply pump 27 is further provided to pass the cold water into the recirculation circuit.
The electrolysis installation is further provided with extinguishing means for inertising the first and second separators when the installation is shut down. The extinguishing means comprise a reserve of pressurised nitrogen 30 and a supply pipe 32 connecting the nitrogen reserve to the two separators 7, 9. When it is sought to shut down the installation, a valve 34 is opened, causing the nitrogen to flow into the separators, preferably in a large amount. Simultaneously, a relief valve 36 on the first separator 7 and the relief valve 23 on the second separator 9 are opened. Thus, the nitrogen exits the first separator through the valve 36, carrying along the hydrogen contained in the separator 7. Similarly, the nitrogen can escape via the valve 23, carrying with it the oxygen contained in the separator 9. This way of proceeding allows the two separators to be emptied and thus in particular allows any risk of explosions, in connection with the presence of hydrogen, to be avoided.
Electrolysis installations of the same type as those that have just been described exhibit some drawbacks. First, the extinguishing means make it necessary to have a large amount of pressurised nitrogen available. Furthermore, the hydrogen contained in the first separator 7 is lost during inertisation because it is mixed with a large amount of nitrogen and then released into the atmosphere.